World population

In demographics, the world population is the total number of humans currently living, and was estimated to have reached 7.7 billion people as of April 2019. It took over 200,000 years of human history for the world's population to reach 1 billion; and only 200 years more to reach 7 billion. The world population has experienced continuous growth following the Great Famine of 1315–1317 and the end of the Black Death in 1350, when it was near 370 million. The highest global population growth rates, with increases of over 1.8% per year, occurred between 1955 and 1975—peaking to 2.1% between 1965 and 1970. The growth rate declined to 1.2% between 2010 and 2015 and is projected to decline further in the course of the 21st century. However, the global population is still increasing and is projected to reach about 10 billion in 2050 and more than 11 billion in 2100. Total annual births were highest in the late 1980s at about 139 million, and as of 2011 were expected to remain essentially constant at a level of 135 million, while deaths numbered 56 million per year and were expected to increase to 80 million per year by 2040. The median age of the world's population was estimated to be 30.4 years in 2018. Six of the Earth's seven continents are permanently inhabited on a large scale. Asia is the most populous continent, with its 4.54 billion inhabitants accounting for 60% of the world population. The world's two most populated countries, China and India, together constitute about 36% of the world's population. Africa is the second most populated continent, with around 1.28 billion people, or 16% of the world's population. Europe's 742 million people make up 10% of the world's population as of 2018, while the Latin American and Caribbean regions are home to around 651 million (9%). Northern America, primarily consisting of the United States and Canada, has a population of around 363 million (5%), and Oceania, the least populated region, has about 41 million inhabitants (0.5%). Though it is not permanently inhabited by any fixed population, Antarctica has a small, fluctuating international population based mainly in polar science stations. This population tends to rise in the summer months and decrease significantly in winter, as visiting researchers return to their home countries. Estimates of world population by their nature are an aspect of modernity, possible only since the Age of Discovery. Early estimates for the population of the world date to the 17th century: William Petty in 1682 estimated world population at 320 million (modern estimates ranging close to twice this number); by the late 18th century, estimates ranged close to one billion (consistent with modern estimates). More refined estimates, broken down by continents, were published in the first half of the 19th century, at 600 to 1000 million in the early 1800s and at 800 to 1000 million in the 1840s. It is difficult for estimates to be better than rough approximations, as even modern population estimates are fraught with uncertainties on the order of 3% to 5%. Estimates of the population of the world at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million. Even earlier, genetic evidence suggests humans may have gone through a population bottleneck of between 1,000 and 10,000 people about 70,000 BC, according to the Toba catastrophe theory. By contrast, it is estimated that around 50–60 million people lived in the combined eastern and western Roman Empire in the 4th century AD.